Dissolved Oxygen

Question 1

Solubility of oxygen

Answer 1

The solubility of oxygen in water increases as the temperature decreases.

Question 2

Oxygen O2

Answer 2

3rd most abundant chemical element. Compromises 21% if the atmosphere

Question 3

Ions

Answer 3

Atoms that have fewer or more electrons, giving a negative or positive charge (cation or anion)

Question 4

Oxidation

Answer 4

Oxygen binding to a molecule, totally changing it’s properties.

Question 5

Chill haze

Answer 5

Polyphenols and proteins bond together to form a colloid when beer is cold, dissolves when beer is warm. Dissolved oxygen helps these molecules bond.

Question 6

Permanent haze

Answer 6

When O2 increases chill haze, rate if conversion into permanent haze will also increase as the bonds between polyphenols and proteins become too big to be insoluble even in warm beer.

Question 7

Reduction in bitterness

Answer 7

Isomerized alpha acids become oxidised as time goes on, changing then and causing bitterness to decline with age.

Question 8

Undesirable flavour compounds as a result of oxidation.

Answer 8

Flavour compounds change it disappear when oxidation/bonded with oxygen. Some become unpleasant, eg lipids which produce E2 nonenal when oxidised (smells and tastes papery)

Question 9

Key control point: seperation

Answer 9

Eg Centrifuge. When DO pick up I’d possible, flush with CO2 and have seals protected by DAW

Question 10

Key control points: cold maturation

Answer 10

Yeast observing O2 is in low concentrations at this stage. As been Cooke, O2 becomes more soluble, and less yeast is available to absorb it.

Question 11

Key control points: clarification

Answer 11

Eg centrifuge after cold maturation before the bright tank. Lower temperatures = higher O2 solubility

Question 12

Key control points: filtration

Answer 12

Powders, sheets, cartridges will contain O2 if not properly deaersted. Sheet filters leak beer continuously throughout the filter run, which can lead to O2 pick up.

Question 13

Key control points: dilution

Answer 13

We must check O2 levels of DAW prior to dilution and O2 levels of diluted beer after.

Question 14

Key control points: packaging

Answer 14

So many places and opportunities for O2 pickup. So many. Valves, unions, pumps, pipes, vessels, process gasses

Question 15

Optochemical oxygen sensor

Answer 15

A sample spread in a layer of plastic containing luminescent dye is illuminated. The oxygen in the sample absorbs some of the energy. The more oxygen, the less light will be measured by the photodetector.

Question 16

Electrochemical oxygen sensor

Answer 16

A cathode (negatively charged electrode) is separated from a sample by a membrane permeable by oxygen. Oxygen that crosses the membrane is given extra electrons. This sensor uses the number of electrons consumed to measure the amount of oxygen in the sample

Question 17

Antioxidants

Answer 17

A compound that stops oxidation reactions usually by becoming oxidised themselves. Sulphur dioxide and potassium metabisulphite most commonly used in brewing.